Even whilst 5G is still being rolled out worldwide, the groundwork for 6G is already being laid, with standards delivery expected around 2030. Data use worldwide is increasing exponentially (rising 15% in the UK between 2022 and 2023 alone), and this will only accelerate with the advent of emerging and future applications, such as autonomous vehicles, smart cities and immersive healthcare. This means that future telecommunications networks will need to deliver a step-change in capability, rather than incremental gains.

Introducing 6G is not only about faster downloads; the vision is for an extremely fast, ultra-reliable, low-latency, and intelligent communication fabric, achieving coverage everywhere and helping to close the digital divide. This network will also need the capacity to accommodate future 6G applications that demand extremely high data rates – and the terahertz (THz) spectrum is emerging as a promising candidate to extend standard technologies into new domains.

What is the THz Spectrum? 

The THz spectrum spans frequencies from around 0.1 THz (100 GHz) to 10 THz, with corresponding wavelengths from about 3 mm down to 0.03 mm – shorter than microwaves, longer than mid-IR/near-IR, and overlapping the far-infrared. What makes THz particularly appealing is the enormous amount of bandwidth available. This allows for ultra-high-speed connectivity, potentially supporting wireless data rates exceeding 100 Gbps – well beyond what is possible with 5G or even advanced mmWave.

Because of this, the THz band has become an active 6G research topic, with engineers and scientists worldwide exploring how it could reshape future mobile networks.

Why THz Spectrum for 6G? 

 The THz spectrum offers:

• Massive bandwidth: Enabling peak throughputs of 100 Gbps and beyond.
• Faster data transmission (lower latency): Because THz provides an exceptionally large bandwidth, each data symbol can be transmitted over a much shorter duration, reducing overall latency. In addition, the very high data rates available at THz frequencies make it possible to send information without compressing it first – avoiding the extra processing time needed for compression and decompression in lower-bandwidth systems.
• Closer integration with optical fibre: THz signals can be generated directly from optical signals by photomixing (where THz radiation is generated by combining two different laser signals on a high-speed optical detector). This makes it possible to create seamless hybrid fibre-wireless networks, combining the reach of optical fibre with the flexibility of wireless.
• Advanced sensing capabilities: Thanks to their very short wavelengths and unique interactions with different materials, THz signals can be used not just for data transfer but also for high-resolution imaging and sensing – enabling applications from gesture recognition to integrated communication-and-radar systems.

These qualities position THz as an enabler of the capabilities policymakers have identified for 6G: intelligence, sustainability, security and universal access.

Utilising the THz spectrum in 6G could also unlock new innovations, including:

• Immersive communication: Holographic conferencing, volumetric (3D) video and ultra-realistic augmented or virtual reality will demand ultra-high-speed connectivity with millisecond latency.
• Data centre connectivity: Short-range high-speed comms using THz links could replace some fibre interconnects, reducing cabling complexity and cost.
• Wireless backhaul: THz could provide fibre-like performance in places where laying fibre is impractical.
• ‘Smart’ applications and automation: By enabling high-resolution sensing, THz could support applications that include ‘Internet of Things,’ ‘smart’ factories and cities, and autonomous driving – areas that require precise motion tracking and/or machine coordination.
• Robotics: Highly-responsive connectivity and integrated sensing could enable advanced robotics, including for healthcare, surgery and industry.

Barriers and Challenges in THz

Despite its promise, THz communications face steep barriers:

• Severe propagation loss: THz signals attenuate rapidly in free space and are highly vulnerable to obstacles and environmental conditions.
• Short transmission ranges: Links are typically limited to tens of metres without special equipment.
• Regulatory uncertainty: Unlike microwaves and mmWave, which already have clearly defined and regulated spectrum allocations, the THz band still lacks globally agreed allocations for communications.
• Device engineering: Generating and detecting THz efficiently requires specialised photonic and electronic devices that are still under development.

HASC Research into THz 

To address these challenges, the Hub in All Spectrum Connectivity (HASC)’s THz research portfolio includes device development, optical-wireless integration and network modelling. Some highlights include:

• THz–Optical Convergence: UCL researchers in HASC, in collaboration with the University of Duisburg-Essen and ACST GmbH, recently demonstrated the conversion of optical fibre signals into THz wireless links, achieving data rates up to 180 Gbps. This shows how existing fibre infrastructure could be seamlessly extended into the THz domain.
• Dark fibre experiments: HASC is investigating the potential of the THz spectrum using the UK’s EPSRC-funded ‘dark fibre’ network. This gives researchers hundreds of kilometres of real-world fibre to test new ideas, such as carrying and regenerating THz signals over long distances to explore how to link high-speed fibre networks with future THz wireless systems.
• Device innovation: A promising technology is the UTC-PD (Uni-Travelling Carrier Photodiode), which converts optical signals into electrical / THz signals. HASC researchers are developing new ways of housing and integrating ultra-fast UTC-PDs, so they deliver more power, handle higher speeds and work more reliably in THz transmitters and receivers.

HASC’s broader portfolio includes advances to provide the underlying capabilities needed to reliably generate, stabilise and harness THz signals within future 6G systems. These include developing methods to create ultra-high-frequency signals by combining laser sources, and designing advanced THz receivers that detect high-frequency signals efficiently and are compact enough for easy integration into real-world systems. Together, these efforts lay the groundwork for turning the promise of THz into practical, everyday 6G connectivity.

6G and Beyond

As the 2030 target for standardising 6G rapidly approaches, the next few years will see THz research move from controlled experiments to field-ready prototypes, allowing researchers to assess how THz can fit into the next-generation communications network. If the attractive qualities of THz are to support the vision for a robust, flexible future telecommunications network, it is vital that the challenges of THz propagation, regulation and device design are addressed.

Ultimately, no single technology will deliver 6G: instead, it is likely this will dynamically integrate THz, mmWave, microwave and legacy frequencies to balance coverage, mobility and capacity. For industry professionals and academics alike, the message is clear: keep watching the terahertz 6G research space. The next generation of wireless is being built now, and the exciting capabilities of THz are starting to take shape.

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